Generally, ceramic wiring substrates are produced by dividing a multi-piece ceramic wiring substrate array into individual pieces along dividing grooves provided on the front surface or back surface of the wiring substrate array. In connection therewith, there has been proposed a method for producing a multi-piece wiring substrate array, in which a blade having a specific edge angle is pressed against a green sheet laminate at positions where specific dividing grooves are to be formed, so that burrs, etc. are less likely to be generated in the vicinity of the thus-formed dividing grooves during formation of individual wiring substrates from the substrate array (see, for example, Patent Document 1).
However, each of the dividing grooves formed by means of the blade has a V-shaped (acute-angled) cross section, and thus a sufficient groove width may fail to be provided between adjacent wiring substrates. Therefore, when adjacent brazing material layers for sealing are melted through heating, the brazing material layers may be accidentally fused together, and the substrate array may fail to be separated into individual wiring substrates.
In addition, since each of the dividing grooves formed by means of the blade has a V-shaped (acute-angled) cross section, when valley folding is performed the side of its front surface having the dividing grooves for separating the substrate array into individual wiring substrates, friction arises between plating films or brazing material layers (for sealing) of a pair of adjacent wiring substrate units, the films or layers being formed on metalized layers on the front surfaces of the wiring substrate units, which may cause problematic damage to the plating film or brazing material layer of each wiring substrate.
Meanwhile, there has been proposed a method for producing a ceramic substrate for division (i.e., a multi-piece ceramic wiring substrate array), in which dividing grooves having no fragile portions in the vicinity of openings thereof are provided by forming a deep and steep narrow portion at the bottom of each groove through a first laser irradiation process, and then forming a pair of chamfered portions at the opening of the narrow portion through a second laser irradiation process (see, for example, Patent Document 2).
However, the production method described in Patent Document 2 also causes problems in that plating films or brazing material layers of the wiring substrate array are damaged due to friction between the films or the layers during formation of individual wiring substrates from the substrate array, and accidental fusion between the brazing material layers cannot be reliably prevented, even when dividing grooves each having a generally Y-shaped cross section are formed through a two-step laser irradiation process, and chamfered portions are formed on both sides of the opening of each groove.